Although semiconductor integrated circuits or semiconductor devices, such as a multilayer interconnect device and the like, are known to have increased power consumption due to leakage current within the interconnect layer insulating film, the overall effect of leakage current on the device (semiconductor device) was small during device generations for which spacing of interconnects forming the semiconductor device exceeded 1 μm. However, as the spacing of interconnects becomes less than or equal to 1 μm, the effect on power consumption has increased due to size reduction of interconnect spacing and an increase of dimensions of interconnects. In particular, when circuits in the future are formed using an interconnect spacing less than or equal to 0.1 μm, leakage current of such interconnects becomes large enough to greatly affect device characteristics and working life.
Presently the damascene method is generally used for interconnect formation of such semiconductor devices. According to the damascene method, a trench shaped like the interconnect is first formed in the insulating film by etching. Thereafter, this method forms a copper interconnect in this trench by plating and the like. However, during interconnect trench formation by etching according to this damascene method, the sidewall of this interconnect trench is readily damaged by etching. Thus leakage current increases due to damage arising in the interior of the insulating film. Also TDDB (Time Dependent Dielectric Breakdown) characteristics worsen due to the occurrence of bowing of the interconnect trench and the like. These phenomena become large factors resulting in lowering of reliability and yield during semiconductor device production.
Here the term “bowing” of the interconnect trench is taken to mean an expansion phenomenon of the trench profile in the lateral direction. This phenomenon can be observed, for example, by slicing the etching trench in the depth direction and then viewing the resultant cross section, as shown in FIG. 1A. In this manner, the cross-sectional profile (i.e., interior of the etching trench) expands in the direction (i.e., lateral direction) indicated by the X arrow. The occurrence of this phenomenon is thought to depend on etching isotropism (i.e., a lack of anisotropy). When such bowing occurs, TDDB characteristics worsen due to narrowing of the effective spacing between interconnects. Furthermore, in FIG. 1A, item 181 is a resist, item 182 is an insulating film, and item 183 is an underlayer of the insulating film. Although for illustrative purposes FIG. 1A shows a profile having the greatest expansion (i.e., removal of the interior wall face of the trench) in the vicinity of the center, since actual etching is isotropic, the trench of insulating film 182 has a shape for which bowing near the resist 181 side is larger than the bowing of the lower layer 183 side.
Due to such circumstances, attention is being paid to technologies for the suppression of damage to the insulating film caused by the etching solution during the interconnect formation process.
As a method for suppression of damage to the insulating film by the etching solution when etching is performed by wet etching, the interconnect trench part of the insulating film has been irradiated with light. The light used for irradiation, for example, is ultraviolet light (UV light). For example, refer to the Japanese Patent Application Laid-Open No. 2001-1724161 and No. 2004-335847. According to these citations, by the use of this method, damage by the etching solution to the interconnect trench sidewall can be suppressed, and an increase of dielectric constant due to moisture can be suppressed.
The above mentioned UV light irradiation is thought to perhaps promote hydrophilicity of the irradiated face, a phenomenon which causes faster etching. That is to say, damage to the interconnect trench sidewall due to etching is not suppressed.
However, performance of etching by wet etching using this type of conventional technology is deficient in that the occurrence of damage to the trench part formed in the insulating film by the etching solution can not be suppressed.